• Untitled Document

    Join us on March 29rd, 7pm EST

    for the CBEC Virtual Meeting

    All EYO members and followers are welcome to join the fun and get to know the guest speaker!

    See the link below for login credentials and join us!

    March Meeting Info

    (dismiss this notice by hitting 'X', upper right)

Mixing types of coax

crznhwy1

Member II
I bought a new vhf antenna from Shakespeare and have installed it on the mast and run the coax to the base. Now I need to run the coax through the cabin. Shakespeare sold the antenna with about 60 ft of RG58c/u coax, but I miss measured how much slack to leave inside the mast and I'm a few feet short of the radio.

I've been trying to find more RG58 locally without any luck. All I can find is RG6 and RG8. So here's the question for the pros out there. Can I match RG58 (50 ohm) with only RG58? Or can I match it with RG8 which is 75 ohm? I will have 35 feet of RG58 running from the masthead to the mast base, then a single run of coax running about 20-25 feet to the radio.

Any suggestions?

Thanks, Mike
 

mherrcat

Contributing Partner
That's a good question and I would like to know the answer, too, as I have just ordered a new VHF radio and plan to install it flush-mount in a panel below the shelf the current radio is now on. The antenna cable just reaches the radio in its current position with about 3" to spare, but the new radio will require about a foot and a half of extra cable.

If it does require an exact match the cable shouldn't be hard to find locally at a good electronics store or probably even at Radio Shack.

I have been told (by satellite engineers) it is better to have a single run of cable with a connector on each end rather than several cables strung together with connectors...
 
Last edited:

u079721

Contributing Partner
I bought a new vhf antenna from Shakespeare and have installed it on the mast and run the coax to the base. Now I need to run the coax through the cabin. Shakespeare sold the antenna with about 60 ft of RG58c/u coax, but I miss measured how much slack to leave inside the mast and I'm a few feet short of the radio.

I've been trying to find more RG58 locally without any luck. All I can find is RG6 and RG8. So here's the question for the pros out there. Can I match RG58 (50 ohm) with only RG58? Or can I match it with RG8 which is 75 ohm? I will have 35 feet of RG58 running from the masthead to the mast base, then a single run of coax running about 20-25 feet to the radio.

Any suggestions?

Thanks, Mike

Well, I also would suggest not mixing impedance. But I might be missing something, because my impression is that RG8 is also 50 ohm impedance so there should be no issue. OTOH, RG6 is 75, so I wouldn't use that.

http://en.wikipedia.org/wiki/Coaxial_cable
 

crznhwy1

Member II
My Radio Shack only carries pre-terminated, pre-packaged RG6 for home video. I remember the day when they were the place to go for electronics parts. Now it's just consumer grade crap and cell phones.
 

Guy Stevens

Moderator
Moderator
RG-8 is 50 ohm.

The RG-8 would work fine for this application.

However it does come is a variety of different constructions, some better for this application than others. In all cases it should work though you may pick up a little more loss with some than others.

Guy
:)
 

Vagabond39

Member III
Coax

Crznhwy1:
If you ran the shakesphere furnished RG 58 down the mast and put a connector on it, attempt to run one continious piece of RG 58 from the mast to your VHF transiever. The fewer connections the less power loss. And more important, the less signal loss from that weak signal needing help. Every connector and impedence mismatch reflects energy back toward the source. Any antenna installation should be checked for a "STANDING WAVE RATIO" and tuned for as close to 1:1 as possible, on the most important frequency.:nerd: That is a measure of reflected power.:mad:
 

mherrcat

Contributing Partner
A quick Internet search shows RG58U and RG8U to both be 50 Ohm impedance, so connecting them should be cool.
 

crznhwy1

Member II
Thanks everyone! I hadn't heard of RG8 until today, so I know where to get it. Can they make more varities of coax? Shees!
 

Guy Stevens

Moderator
Moderator
SWR Meter

A device called an swr meter.

They come in several varieties, the one that you would need is the one that covers the frequency range of 156–162 Mega-Hertz.

There are a variety of them, most of the good ones are about $100.00 or so. There is a company called MFJ that makes some at the $50.00 range, but they have a habit of shipping items that do not function at all.

The standard CB SWR meters that you can get for about $10.00 anywhere will not work correctly for the frequency range that we are operating at with a marine VHF.

Guy
:)
 
Last edited:
Top